Here is an interesting project. A portable rail gun that was mostly 3D printed.

Below is the CAD drawing. Everything in gray was 3D printed.

The blue capacitors combined weight is 20 lbs. It looks like a Neill Blomkamp weapon from District 9.

Here are the projectiles. The railgun is capable of firing copper plated tungsten, aluminum, carbon and teflon/plasma. Here we have copper plated tungsten armatures.

You can check out a breakdown of the build here.

Thanks to Bryan S. for the hat tip.